Apple seeded its developers with the third beta of iPhone OS 4 yesterday. The release sports a few previously unknown features, including file sharing between the supported iPhone apps and desktop iTunes, a better way to kill running tasks, a brand new orientation lock feature, and more.

iPhone OS 4 is coming along pretty well. According to web reports, Beta 3 has a few loose ends but runs noticeably smoother than the previous release. The iPhone OS 4 Beta 3 release notes state that Apple fixed both the camera issue (photo and video) and screenshot-taking functionality. More interesting are the features Apple wants to keep secret until the software is officially released for the iPhone in iPod touch in June (iPad release is due in Fall).

Thanks to eagle-eyed bloggers who relentlessly scavenge build files for clues, we can report about the following features that could become a part of the official iPhone OS 4 feature set:

iPod widget and orientation lock – Swiping left on your first home screen in iPhone OS 3 takes you to the Spotlight search interface. Doing the same thing on the multitasking interface in iPhone OS 4 reveals five special icons that let you launch the iPod app, control music playback (play/pause, skip forward/backward), and locks your device in portrait mode – nice!

Closing running tasks – Double-pressing the home button invokes an app tray at the screen bottom containing a swipeable icons that represent your running tasks. The new build lets you close any running task by tapping its quit badge, similar to removing apps from your home screen. You can also tap and hold any icon to show close badges on all the icons, allowing you to quickly kill a bunch of apps.

File sharing – Looks like iPhone OS 4 will let you drop files from your desktop to apps that support this feature and vice versa. The feature behaves like on an iPad running iPhone OS 3.2, via desktop iTunes, meaning you can only access an app-specific file storage rather than the entire file system.

Facebook integration – This one actually appeared in the previous beta, but it’s cool knowing that Apple might in fact integrate Facebook on the system level, like on BlackBerries. A generic “SocialKitInternal.framework” revealed in the third beta suggests all kinds of things, from the ability to upload photos to Facebook and change your profile picture to mergingyour Facebook friends with Address Book contacts.